Electrical Transport Properties Of SnS₂ Under High Pressure

Band structure engineering on TMDs allows ones to explore exotic condensed matter phenomena and develop many potential applications.For example,the mod-ification of their band structures from indirect-band-gap to direct-band-gap provides insights into opto-electronics and valley electronics.Tin disulfide(SnS2)is an emerg-ing semiconductor metal disulfide.This compound has received significant attention due to the unique properties arising from the layered structure of SnS2,including relatively high carrier mobility and exceptionally large excitonic effects.SnS2 is a multifunctional material that can be used in many applications such as thermo-electricity,photocatalytic,gas sensing,etc.,with great potential application value Compared with the other methods,high pressure is a powerful way to induce dra-matic changes in their crystal structures and electronic structures.In our work,high pressure up to 25.0GPa was generated by a diamond anvil cell(DAC).the electrical transport properties of nano-level SnS2 including the measurement of in situ resistivity and AC impedance spectrum under high pressure have been studied The surface morphology analysis of SnS2 under environmental pressure and after pressurization has been investigated by scanning electron microscopy(SEM)and the first principle was used to calculate the energy band structure and density of states of SnS2 at different pressure points.The abnormal behavior and pressure effect-s of the electrical transport properties of SnS2 samples under high pressure were determined.Surprisingly,both experiment and calculation show that the limited pressure strongly modulates its band structure does not bring the transition from a semiconductor to metal.The results are listed as follows:An in-situ electrical resistivity measurement of SnS2 has been conducted in a DAC up to 25.0GPa,and the variation law of the resistivity under pressure is obtained:The resistivity of SnS2 decreased by three orders of magnitude over the entire pressure range,and the lowest resistivity reached 25.964?·cm.In the range of 0-4.4Gpa,the sample powder became tighter with increasing pressure,the dis-tance between atoms continued to decrease,and the sample resistivity decreased.Gradually,the interlayer interaction increases due to the interlaminar compression mechanism in the range of 4.4GPa to 11.2GPa.The resistivity increases by an order of magnitude to show an abnormal reversal,and then gradually decreases as the pressure continues to increase until 25.OGPa.The in-situ AC impedance spectrum of SnS2 sample was measured,and the impedance spectrum and total resistance of the sample were obtained within 16.4G-Pa.In the range of 4.4GPa,the resistance gradually decreases.The Nyquist spec-trum consists of two parts respectively are the semiarc of the high-frequency region and the curve of the low-frequency region,which means the conduction process of the charge carriers inside the grain,and the space charge dissipated at the grain boundaries.Then there is only one semi-circular arc in the impedance plane to indi-cate grain conduction,and the resistance gradually increases in the range of 4.4GPa to 11.2GPa.In the range of 11.2GPa to 16.4GPa,the resistance gradually decreases.The trend of impedance spectrum is consistent with the trend of resistivity change.The equivalent impedance circuit is used to simulate the measured impedance spec-trum,and the change law of the total resistance is obtained.The total resistance decreases gradually with the increase of pressure before 4.4GPa,and increases with the increase of pressure in the range of 4.4GPa to 11.2GPa.The trend showed an abnormal reversal,showing a downward trend with increasing pressure in 11.2GPa to 16.4GPa.The first principle is used to calculate the energy band and density of states within 20.0GPa of SnS2.We used Heyd-Scuseria-Ernzerhof(HSE)method instead of local density approximation(LDA)to avoid low bandgap calculations,and ob-tained more accurate calculation results:Under the action of pressure,the band gap of SnS2 gradually decreases,which is 3.081eV at OGPa,and at 20.0GPa,the energy gap is reduced to 1.517eV.